The proposed research is designed to investigate the physiological determinants of aggressive behavior in two rodent species in which both sexes are aggressive; the golden hamster and the Mongolian gerbil. Experiments are proposed to investigate the role of the medial preoptic area and anterior hypothalamus in aggressive sexual behavior in male and female hamsters. Furthermore, in hamsters, experiments investigating the influence of estrogen antagonists and nonaromatizable androgens on aggression are proposed. In gerbils, experiments investigating the interaction of hormonal state and social history on aggression are described. The undersigned agrees to accept responsibility for the scientific and technical conduct of the project and for provision of required progress reports if a grant is awarded as the result of this application.